In the fields of aircrafts, ships, vehicles, and the like, a composite material made of fiber reinforced plastics (FRP) is widely used as a structure increased in strength and reduced in weight. Holes are sometimes formed in such a composite material for inspection and for access during assembly. When the holes are formed, since stress concentration occurs in the peripheral edge portions of the holes, it is necessary to increase the strength of the peripheral edge portions of the holes.
PTL 1 described below discloses an invention for adding a reinforcing layer to increase thickness and increasing strength in order to reinforce the peripheral edge portions of access holes of an outer plate of an aircraft. The reinforcing layer described in PTL 1 is fixed to a base material by pins or stitches to prevent the reinforcing layer from peeling when the reinforcing layer receives a load.